The present invention relates to a method for detecting a short circuit within an energy store.
In electrochemical energy stores such as, for example, battery cells, which are used nowadays, undesired, potentially dangerous reactions of the energy store can occur when cell faults occur. In particular, the electrically conducive connections which occur within the energy store, for example internal short-circuits, short-circuits to ground or soft short circuits, represent a specific potential hazard, since as a result of an undesired current flow in the energy store the energy store can heat up strongly. It is therefore possible, for example, for strong heating of individual battery cells or a plurality of battery cells that occur in the battery module. Owing to this heating, when a critical temperature, in particular, a cell temperature is exceeded, a self-sustaining exothermic reaction of a battery cell can be triggered. This is also referred to as a thermal runaway. Cases in which burning and/or explosion of a cell has occurred as a result of such cell faults are known.
The potential hazard of electrochemical primary stores and secondary stores and the effects of a fault situation on persons, asset values and the environment is known.
The possible hazards posed by electrochemical energy stores are a challenge, in particular in the case of energy stores for electromobility applications such as, for example, passenger cars, trucks or transportation vehicles which are each equipped either with a fully electric drive or an electrically assisted drive. Battery systems in such applications often have to make available a high power level and a high level of stored energy and as a result involve a high potential hazard. However, at the same time stringent requirements are made of the safety of the energy store which are taken into account when designing the battery system. In particular for high-power cells and high-energy cells in the applications mentioned above it is desirable to detect cell faults which occur as early as possible and with a high level of reliability in order to avoid dangerous situations by warning the user and/or by means of technical counter measures.
Contemporary battery systems for use in electrical mobility are usually composed of a series circuit of a plurality of battery cells. The battery cells are usually combined in battery modules which are provided with a sensor system for monitoring the cells. A plurality of battery modules form a battery system. A central control unit of the battery system combines the signals of the sensor system in the battery modules and further sensor signals and implements simple control actions such as, for example, the complete switching off of the battery system in a fault situation. The cells in such battery systems are often high-power/high-energy cells in a specific design. The specific design is often distinguished by prismatic housings made of aluminum alloys or stainless steel. At present, lithium ion cells are usually used for the specified applications.
Methods for detecting a short circuit are known from US2010/0188054, US2010/0194398 and US2011/0148426.